Geopolymers for the removal of pharmaceuticals from water: mechanistic insights and comparative performance

Abstract

Pharmaceutically active compounds (PhACs) are increasingly detected in surface waters and treated effluents. However, their removal during conventional treatment remains inconsistent because of their recalcitrance and variable speciation. Geopolymers offer a sustainable remediation solution, as they are highly tunable and can be synthesised from low-cost aluminosilicate precursors, including industrial byproducts. Nevertheless, research on geopolymer–PhAC is fragmented. Adsorption studies are often conducted in simplified batch systems, and photocatalysis data tend to focus on antibiotics. This review aims to consolidate and critically assess geopolymer-based adsorption and geopolymer-supported photocatalysis for PhAC removal. Emphasis is on the mechanistic connections between PhAC descriptors, geopolymer characteristics, and process variables. Adsorption performance ranges from 19–99% removal, showing significant sensitivity to pH-driven electrostatics. Photocatalytic systems typically exhibit tighter performance distributions and higher removal rates (> 90%). This is due to enhanced charge transfer and radical generation at the geopolymer and the semiconductor interface. A comparative synthesis indicates a higher median parent-compound removal rate for photocatalysis (93.44%) than for adsorption (86.0%) in the assembled dataset. Finally, the review outlines future research directions, including the development of standardised datasets, chemically informed PhAC descriptors, explainable machine-learning frameworks, validation with real wastewater, mineralisation assessment, and continuous-flow testing. These steps are necessary to support the transition of geopolymer-based PhAC treatment from laboratory studies to practical wastewater applications.